Wednesday, April 26, 2017

Furthermore, phylogenetic analyses that incorporate sufficient character data are able to differentiate the members of such paravian lineages as Dromaeosauridae, Troodontidae and Avialae, as demonstrated by our present study. Nevertheless, reinterpretation of Balaur as a flightless avialan reinforces the point that at least some Mesozoic paravian taxa, highly similar in general form and appearance to dromaeosaurids, may indeed be the enlarged, terrestrialised descendants of smaller, flighted ancestors, and that the evolutionary transition involved may have required relatively little in the way of morphological or trophic transformation.

Fossil
evidence for changes in dinosaurs near the lineage leading to birds and the
origin of flight has been sparse. A dinosaur from Mongolia[Mahakala] represents the basal divergence within Dromaeosauridae. The taxon's small body
size and phylogenetic position imply thatextreme
miniaturization was ancestral for Paraves(the clade
including Avialae, Troodontidae, and Dromaeosauridae), phylogenetically earlier
than where flight evolution is strongly inferred. In contrast to the sustained
small body sizes among avialans throughout the Cretaceous Period, the two
dinosaurian lineages most closely related to birds, dromaeosaurids and
troodontids, underwent four independent events of gigantism, and in some
lineages size increased by nearly three orders of
magnitude.

So there is evidence of secondarily flightless paravians.
Let us now tie this with the issue of the statistically poorly supported core nodes. (See earlier posts).
Let's look at Pennaraptora. Pennaraptora is particularly poorly supported. Consequently Oviraptors may not be related to Paraves as sister taxa as commonly presented. Instead, Oviraptorids (that are dated 10's of millions of years later than basal Paraves) may well be secondarily flightless members of Paraves. And in fact that idea has been proposed over the years.

Halszka Osmólska et al. (2004) ran a cladistic analysis that came to a different conclusion. They found that the most birdlike features of oviraptorids actually place the whole clade within Aves itself, meaning that Caudipteryx is both an oviraptorid and a bird. In their analysis, birds evolved from more primitive theropods, and one lineage of birds became flightless, re-evolved some primitive features, and gave rise to the oviraptorids. This analysis was persuasive enough to be included in paleontological textbooks like Benton's Vertebrate Paleontology (2005).[11]The view that Caudipteryx was secondarily flightless is also preferred by Gregory S. Paul,[12]Lüet al.,[13] and Maryańskaet al.[14]

The evidence all points to Oviraptorids being secondarily flightless members of derived Paraves. And of course, a few established researchers had already come to that conclusion.
The same logic applies to Ornithomimosaurs (as being secondarily flightless members of derived Paraves).

Paul (2002) has argued that
the reason some maniraptoran taxa possess so
many derived avian apomorphies is that they are,
in fact, secondarily flightless birds that are more
derived than basal avian taxa like Archaeopteryx.
Although Paul (2002) retained a theropod ancestry
for birds, support for his hypothesis would
clearly complicate the consensus BMT view. A
few cladistic analyses have retrieved Alvarezsauridae
(e.g., Perle et al. 1993, 1994; Chiappe
et al. 1998) and Oviraptorosauria (Lü et al. 2002,
Marya´nska et al. 2002) as birds more derived
than Archaeopteryx, and other noncladistic studies
have proposed avian status for various oviraptorosaur
(Elzanowski 1999, Lü et al. 2005) and
dromaeosaur taxa (Czerkas et al. 2002, Burnham
2007). These studies have provided support for
elements of Paul’s (2002) hypothesis.

Oviraptorosaurs, like deinonychosaurs, are so bird-like that several scientists consider them to be true birds, more advanced than Archaeopteryx. Gregory S. Paul has written extensively on this possibility, and Teresa Maryańska and colleagues published a technical paper detailing this idea in 2002.[5][16][17]Michael Benton, in his widely respected text Vertebrate Paleontology, also included oviraptorosaurs as an order within the class Aves.[18] However, a number of researchers have disagreed with this classification, retaining oviraptorosaurs as non-avialan maniraptorans slightly more primitive than the deinonychosaurs.[19]

The presence of numerous flight features reveal that Caudipteryx, like the extant flightless ratites, originated from volant ancestors (de Beer 1956; Feduccia 2012, 2013), most likely via the evolutionary process of heterochrony, specifically paedomorphosis (arrested development), by which the adult retains the morphology of a younger stage of development (Livesey 1995).

Reinterpretation of the Early Cretaceous maniraptoran
(Dinosauria: Theropoda) Zhongornis haoae as a
scansoriopterygid-like non-avian, and morphological
resemblances between scansoriopterygids and basal
oviraptorosaurs The condition present in
Zhongornis resembles that seen in scansoriopterygids (Epidendrosaurus, Epidexipteryx) and
basal oviraptorosaurs (Caudipteryx), which also have proportionately short tails compared to
basal paravians

The past two decades have witnessed the collapse of every single classical autapomorphy (or “holodiagnostic” to use Charig’s term) of Aves, from furculae, to feathers. Accordingly, distinguishing a par-avian theropod from a bona fide bird, is increasingly a matter of subjectivity. Add into this mess the argument that taxa traditionally classified as lying outside Aves are in fact neoflightless forms closer to Neornithes than is Archaeopteryx, and you have enough to drive the prospective student of avian phylogenetics to despair.

In order to test previous suggestions that oviraptorosaurs might be basal avialans, we ran two
additional analyses. The first of these analyses was constrained to produce a monophyletic
group comprising all oviraptorosaurian and non-archaeopterygid avialan species, whereas the
second was constrained to produce a monophyletic group comprising all oviraptorosaurian
and avialan including archaeopterygid species. The first analysis resulted in 1096 most
parsimonious trees, each having a length of 1410 steps. Figure S10 shows the strict consensus
of the 1096 trees. The second analysis resulted in 216 most parsimonious trees, each having a
length of 1413 steps. Figure S11 shows the strict consensus of the 216 trees. These analyses
indicate that the hypotheses that recover an Oviraptorosauria-Avialae clade are considerably
less parsimonious than the hypothesis shown in Figure 6. However, one reason that the
Oviraptorosauria-Avialae hypotheses are worse supported by our dataset might be the large
amount of missing data from the palates and braincases of the basal oviraptorosaurs and basal
avialans, regions that represent important sources for oviraptorosaurian synapomorphies.

In oviraptorosaurs and basal avialans the
supraacetabular crest is absent.

The remaining maniraptorans form the clade Pennaraptora ("feathered raptors"). These comprise the oviraptorosaurs, the scansoriopterygids, and the eumaniraptorans. These groups are united by several important characteristics:

Thursday, April 20, 2017

We have seen that the statistical support values do not support the dinosaur to bird hypothesis. See earlier posts.
Consequently we are justified in looking at the dinosaur to bird hypothesis much more critically and to re-assess the explanations that have been given. For example, the "explanation" that the evolution rate was abnormally rapid.

"Relative to the femur, the humerus is significantly longer and thicker in basal paravians than in non-paravian theropods." (Xu et al)
"The significant lengthening and thickening of the forelimbs indicates a dramatic shift in forelimb function at the base of the Paraves." (Xu et al)
"We find an increase in rates of body size and body size dependent forelimb evolution leading to small body size relative to forelimb length in Paraves." (Puttick et al)

"We were really surprised to discover that the key size shifts [body size and forelimb length] happened at the same time,at the origin of Paraves," said Mr Puttick of Bristol's School of Earth Sciences. "This was at least 20 million years before the first bird, the famous Archaeopteryx, and it shows that flight in birds arose through several evolutionary steps."

As the quotes above show, basal paravians are very different than non-paravian theropods. The researchers who believe they are related, explain this as an "abnormally rapid period of morphological evolution". Of course that is not an explanation. It is an acknowledgement that they have no explanation.

Our results demonstrate that the rise of birds was a complex process: birds are a continuum of millions of years of theropod evolution, and there was no great jump between nonbirds and birds in morphospace, but once the avian body plan was gradually assembled, birds experienced an early burst of rapid anatomical evolution.

Although birds are clearly distinct compared to all other living vertebrates, the avian bauplan isn’t especially distinct relative to other coelurosaurs, particularly their closest relatives.

There is growing evidence that changes in discrete character evolution, body size, and limb anatomy occurred quickly in the vicinity of the origin of birds, either at the node Avialae, in close avialan outgroups [basal paraves] or beginning with slightly more derived birds [3, 4, 5, 6, 19, 20, 21, 22]. It is likely that different types of data will pinpoint changes at slightly different positions on phylogeny, but in general, recent studies converge in identifying the dinosaur-bird transition as an abnormally rapid period of morphological evolution.

The initial results of the branch (Dryad Fig. S4-13) and clade (Fig. S3; Dryad Fig. S14-23) tests strongly support significantly high rates in Avialae, and to a lesser degree Tyrannosauroidea.

forelimbs are optimized in our analysis as a primitive character state

for the Paraves (see Supplementary Information). The significantlengthening and thickening of the forelimbs indicates a dramatic shiftin forelimb function at the base of the Paraves, which might be related

to the appearance of a degree of aerodynamic capability.

We use the ratios of humeral length to femoral length, and humeral diameter to femoral diameter, as indicators of forelimb length and robustness. Relative to the femur, the humerus is significantly longer and thicker in basal paravians than in non-paravian theropods, derived dromaeosaurids and troodontids (the relatively short and slender forelimbs in the last two groups are secondarily evolved according to the current phylogenetic analysis).

Although there is no overall theropod-wide trend (fig. S7 and SM, part D), there is an exceptional trend within the single lineage that comprises much of the avian stem.

Our study quantifies rates of evolutionary innovation in dinosaurs using 1549 (data set 1) and 421 (data set 2) skeletal and other anatomical traits distributed across the entire body. A clear pattern emerges: Branches along the bird stem undergo substantially faster morphological evolution than those of the rest of the tree.

Recent discoveries have highlighted the dramatic evolutionary transformation of massive, ground-dwelling theropod dinosaurs into light, volant birds. Here, we apply Bayesian approaches (originally developed for inferring geographic spread and rates of molecular evolution in viruses) in a different context: to infer size changes and rates of anatomical innovation (across up to 1549 skeletal characters) in fossils. These approaches identify two drivers underlying the dinosaur-bird transition. The theropod lineage directly ancestral to birds undergoes sustained miniaturization across 50 million years and at least 12 consecutive branches (internodes) and evolves skeletal adaptations four times faster than other dinosaurs. The distinct, prolonged phase of miniaturization along the bird stem would have facilitated the evolution of many novelties associated with small body size, such as reorientation of body mass, increased aerial ability, and paedomorphic skulls with reduced snouts but enlarged eyes and brains.

These results reconcile contradictory studies
identifying presence (4–8) or absence (9–11) of
a trend toward size reduction in theropods. Although
there is no overall theropod-wide trend
(fig. S7 and SM, part D), there is an exceptional
trend within the single lineage that comprises
much of the avian stem.

That shrinkage sped up once bird ancestors grew wings and began experimenting with gliding flight. Last year, Benton’s [Puttick] team showed that this dinosaur lineage, known as paraves, was shrinking 160 times faster than other dinosaur lineages were growing. “Other dinosaurs were getting bigger and uglier while this line was quietly getting smaller and smaller,” Benton said. “We believe that marked an event of intense selection going on at that point.”

Mark Puttick and colleagues investigated the rates of evolution of the two key characteristics that preceded flight: body size and forelimb length. In order to fly, hulking meat-eating dinosaurs had to shrink in size and grow much longer arms to support their feathered wings.

"We were really surprised to discover that the key size shifts happened at the same time,at the origin of Paraves," said Mr Puttick of Bristol's School of Earth Sciences. "This was at least 20 million years before the first bird, the famous Archaeopteryx, and it shows that flight in birds arose through several evolutionary steps."

The origin of birds (Aves) is one of the great evolutionary transitions. Fossils show that many unique morphological features of modern birds, such as feathers, reduction in body size, and the semilunate carpal, long preceded the origin of clade Aves, but some may be unique to Aves, such as relative elongation of the forelimb. We study the evolution of body size and forelimb length across the phylogeny of coelurosaurian theropods and Mesozoic Aves. Using recently developed phylogenetic comparative methods, we find an increase in rates of body size and body size dependent forelimb evolution leading to small body size relative to forelimb length in Paraves, the wider clade comprising Aves and Deinonychosauria. The high evolutionary rates arose primarily from a reduction in body size, as there were no increased rates of forelimb evolution. In line with a recent study, we find evidence that Aves appear to have a unique relationship between body size and forelimb dimensions. Traits associated with Aves evolved before their origin, at high rates, and support the notion that numerous lineages of paravians were experimenting with different modes of flight through the Late Jurassic and Early Cretaceous.

The taxon's small body size and phylogenetic position imply that extreme miniaturization was ancestral for Paraves (the clade including Avialae, Troodontidae, and Dromaeosauridae), phylogenetically earlier than where flight evolution is strongly inferred. In contrast to the sustained small body sizes among avialans throughout the Cretaceous Period, the two dinosaurian lineages most closely related to birds, dromaeosaurids and troodontids, underwent four independent events of gigantism, and in some lineages size increased by nearly three orders of magnitude.

Note

This site presents the idea that pterosaurs (rather than dinosaurs) developed into birds. This is not an "evolutionism" vs. "creationism" issue.An "evolutionist" can say that the pterosaur to bird developments are due to neo-Darwinian means (random mutation and natural selection).On the other hand, a "creationist" can say that those developments are the acts of a higher intelligence.This site does not take a position on the "evolutionism" vs. "creationism" question.

Philosophy

Like most people, I have philosophical ideas that go beyond the nuts and bolts of the scientific analysis of the origin and development of birds.There are larger questions that philosophers have grappled with since the most ancient times. If anyone is interested in my take on those more philosophical ideas, click here.But please realize that all the ideas of this site are pure materialist, scientific ideas supported by physical evidence and scientific studies.

The 19th-century German philosopher Arthur Schopenhauer astutely summarized the three stages through which all truth passes: first, it is ridiculed; second, it is violently opposed;

and third, it is accepted as being self-evident.

"In the choice between changing one's mind and proving there's no need to do so, most people get busy on the proof."~John Kenneth Galbraith

Keywords

origin of birds, pterosaur is the ancestor of modern birds, birds did not evolve from dinosaurs, cladistics, stratocladistics, Cretaceous, Mesozoic, fossil record, BAD, BAND, birds are not dinosaurs, flightless birds, aves